In this study, for the first time, NO production by the central nervous systems has been directly demonstrated in invertebrate species. N-methyl-D-glutamine was used as the spin trap for trapping NO. EPR study was conducted on X-band. Quartz flat cell was used as sample holder. Five molluscan species, known to be widely used as neurobiological experimental models have been investigated: Aplysia californica, Pleurobranchaea californica, Planorbarius corneus, Octopus vulgaris.